Copper-zinc-aluminum catalysts have been used for water gas shift reaction, methanol synthesis reaction, or production of an aldehyde or a ketone by alcohol dehydrogenation; or used as a hydrogenation catalyst or a desulfurization catalyst. However, copper-zinc-aluminum catalysts are likely to be impaired due to copper or zinc aggregation. Therefore, demand has arisen for improvement of durability of such catalysts.
As has been conventionally known, water gas shift reaction is an important reaction for removal of carbon monoxide upon production of hydrogen from a hydrocarbon, or for regulation of the ratio of hydrogen to carbon monoxide in methanol synthesis or oxo reaction. Recently, water gas shift reaction has become of interest as a reaction for producing, from a hydrocarbon or a similar material, hydrogen which is used for fuel cells and has a lowered carbon monoxide concentration.
Hitherto, iron-chromium catalysts have been developed for high-temperature water gas shift reaction, whereas copper-zinc-aluminum oxide catalysts have been developed for low-temperature water gas shift reaction. Various attempts have been made to improve the activity or durability of such a catalyst.
Specifically, Patent Document 1 discloses a catalyst for water gas shift reaction exhibiting good catalytic activity, the catalyst being prepared by introducing alumina or alumina gel (i.e., an alumina precursor) into a reaction system in advance, and forming copper and zinc precipitates around the alumina or alumina precursor serving as a nucleus. Patent Document 2 discloses a catalyst for CO shift reaction, which catalyst contains, as essential components, copper oxide, zinc oxide, aluminum oxide, zirconium oxide, and manganese oxide, and which exhibits a CO conversion higher than that of a conventional catalyst for low-temperature CO shift reaction containing copper/zinc/aluminum oxide. Patent Document 3 discloses a catalyst for low-temperature water gas shift reaction, which catalyst exhibits excellent activity and stability, which contains specific amounts of copper oxide, zinc oxide, and aluminum oxide, and which is produced from a precursor substance containing aluminum in the form of hydrotalcite and aluminum in a form different from hydrotalcite. Patent Document 4 discloses a method for synthesizing methanol by use of a copper-zinc catalyst produced from a catalyst precursor of aurichalcite-crystal-form ((Cu, Zn)5(CO3)2(OH)6). However, there has not yet been reported a methanol synthesis method by use of a copper-zinc-aluminum catalyst precursor exhibiting an X-ray diffraction pattern of spertiniite-crystal-form (Cu(OH)2) or hydroscarbroite-crystal-form (Al14 (CO3)3(OH)36·n(H2O)). Patent Document 5 discloses a carbon monoxide conversion catalyst exhibiting high activity at low temperature, which catalyst is prepared through a coprecipitation process in which an aqueous metal solution containing copper and zinc is mixed with a basic aqueous solution containing at least one of a primary amine, a secondary amine, and a tertiary amine. Patent Document 6 discloses a catalyst for carbon monoxide conversion, which catalyst can maintain high carbon monoxide conversion over a long period of time at a relatively low temperature, and which is produced through calcining of a composition containing specific amounts of copper oxide, zinc oxide, and silicon oxide.
However, none of the above-disclosed catalysts is satisfactory as a catalyst for water gas shift reaction for producing hydrogen used in a fuel cell, which is turned on and off frequently and repeatedly.    Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2003-236382    Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. 2004-122063    Patent Document 3: Japanese Patent Application Laid-Open (kokai) No. 2005-520689    Patent Document 4: Japanese Patent Application Laid-Open (kokai) No. H09-187654    Patent Document 5: Japanese Patent Application Laid-Open (kokai) No. 2004-298685    Patent Document 6: Japanese Patent Application Laid-Open (kokai) No. 2000-126597